/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.event;

import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.core.Ordered;
import org.springframework.core.ResolvableType;
import org.springframework.lang.Nullable;

/**
 * {@link org.springframework.context.ApplicationListener} decorator that filters
 * events from a specified event source, invoking its delegate listener for
 * matching {@link org.springframework.context.ApplicationEvent} objects only.
 *
 * <p>Can also be used as base class, overriding the {@link #onApplicationEventInternal}
 * method instead of specifying a delegate listener.
 *
 * @author Juergen Hoeller
 * @author Stephane Nicoll
 * @since 2.0.5
 */
public class SourceFilteringListener implements GenericApplicationListener, SmartApplicationListener {

    private final Object source;

    @Nullable
    private GenericApplicationListener delegate;


    /**
     * Create a SourceFilteringListener for the given event source.
     *
     * @param source the event source that this listener filters for,
     * only processing events from this source
     * @param delegate the delegate listener to invoke with event
     * from the specified source
     */
    public SourceFilteringListener(Object source, ApplicationListener<?> delegate) {
        this.source = source;
        this.delegate = (delegate instanceof GenericApplicationListener ?
                         (GenericApplicationListener) delegate : new GenericApplicationListenerAdapter(delegate));
    }

    /**
     * Create a SourceFilteringListener for the given event source,
     * expecting subclasses to override the {@link #onApplicationEventInternal}
     * method (instead of specifying a delegate listener).
     *
     * @param source the event source that this listener filters for,
     * only processing events from this source
     */
    protected SourceFilteringListener(Object source) {
        this.source = source;
    }


    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        if (event.getSource() == this.source) {
            onApplicationEventInternal(event);
        }
    }

    @Override
    public boolean supportsEventType(ResolvableType eventType) {
        return (this.delegate == null || this.delegate.supportsEventType(eventType));
    }

    @Override
    public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
        return supportsEventType(ResolvableType.forType(eventType));
    }

    @Override
    public boolean supportsSourceType(@Nullable Class<?> sourceType) {
        return (sourceType != null && sourceType.isInstance(this.source));
    }

    @Override
    public int getOrder() {
        return (this.delegate != null ? this.delegate.getOrder() : Ordered.LOWEST_PRECEDENCE);
    }


    /**
     * Actually process the event, after having filtered according to the
     * desired event source already.
     * <p>The default implementation invokes the specified delegate, if any.
     *
     * @param event the event to process (matching the specified source)
     */
    protected void onApplicationEventInternal(ApplicationEvent event) {
        if (this.delegate == null) {
            throw new IllegalStateException(
                    "Must specify a delegate object or override the onApplicationEventInternal method");
        }
        this.delegate.onApplicationEvent(event);
    }

}
